In 1945, Hiroshima, Japan, was a city of about 255,000 people that was largely untouched by the war, according to a paper in the American Journal of Epidemiology (opens in new tab). The damage caused by the Hiroshima bombing (Image credit: Getty/ Bettmann / Contributor) Army's Manhattan District, the name Manhattan Project eventually stuck, though work was carried out in Los Alamos, New Mexico Oak Ridge, Tennessee Hanford, Washington Chalk River, Ontario, and several other sites, according to The Bradbury Science Museum (opens in new tab).Īfter several years of intensive research under strict secrecy, the Manhattan Project developed two different bombs that used two different nuclear materials: uranium-235 and plutonium-239, according to the US Department of Energy (opens in new tab). One scientist denied clearance to work on the project was Albert Einstein, according to The American Museum of Natural History (opens in new tab).īecause one early component of the project was based in the U.S. Within a matter of months, a coalition of American, British and European scientists - many of whom were refugees from Germany, Italy and other fascist nations - began collaborating on a vast international project to develop a uranium-based bomb before any Axis powers beat them to it.
